Interestingly most of the flip up helmets are not tested with the front them flipped up but I have often seen the police using theirs fully opened up. Apparently they have been tested with them down or with some types, with the front removed.
I have used them for 6-7 years and prefer them to fixed or open face helmets.
Some of them are more fashion than practical. For instance roof helmets look good but mist up too easily in cold weather.
I have even seen one that looks like a full lid but the bottom chin bar was really soft plastic, no idea what that was about.
There is also one open face helmet that has a solid bar for a chin guard
I use a caberg which I am happy with most of the time, it does tend to mist up and I wouldn't buy a matt helmet again. It has become very marked and looks shabby but has never been droped etc.
The best feature is that they have a flip down extra dark visor which is good to have when going into the sun. ( I have also been told that the observations of type 4 hazards can be more easily done with the dark visor down

)
Many of the flip helmets also have not been approved by ACU for track use.
I liked the shoe helmet but was more money than I could afford.
beeman